Hardwood is great for rentals because of the durability so I'd sand/re-condition the existing floor (if it's in decent shape).

The boiler heats all 3 units and was reconditioned in 2014..the current seller/owner says that the monthly heat and water bills average out to about $250 a month over the course of the year. 

Nevertheless, that can be way off under current RE conditions.

I updated the kitchen from original 1980's stained wood cabinates and laminent counter tops by reconditioning the cabinates (painting the uppers white with crown moulding, slate for lowers, and installing gold hardware), hand-pouring a white with black marble-type epoxy over the existing counter tops, installing white subway tile with black grout, and removing a large section of cabinates and replacing them with floating shelves.We insulated and heated the former 3-seasons room and converted i What was the outcome?

I updated the kitchen from original 1980's stained wood cabinets and laminate countertops by reconditioning the cabinets (white, slate, and gold), hand-pouring a white with black marble-type epoxy over the existing countertops, installing white subway tile with black grout, and removing a large section of cabinets and replacing them with floating shelves.I also added a 250 sq. ft. bedroom by heating and insulating the three-season room/office.What was the outcome?

I buy good, used reconditioned appliances from the Habitat for Humanity and they've never sold me a lemon. 

Attending workshops or conferences, and listening to podcasts, Ted talks, and audiobooks will also help change and recondition one’s mind.

I would build the cost of cleaning carpets between tenants into the cost of the one year lease, put in an early termination fee of X amount to cover reconditioning and vacancy time if they stay less than a year, and make the deposit just that, a security deposit. 

Used appliance stores will take appliances that they can recondition and resell.

For the average sized kitchen, you're looking at $2k to recondition and paint professionally.